in order for the self-leveling novimat shocks to function properly, the springs are a little softer. if u had gone with just shocks upgrade to something that wasn't self-leveling, ur rear would actually sag. hmm...=). anyway, so basically ipd's springs would probably be too stiff, hence, u need to replace the rear. given what u've stated, H&R springs for self-leveling rears would be fine.